This invention relates to grey glass compositions and methods of making the same. More particularly, this invention relates to erbium-containing grey glass compositions having low light transmittance in the UV (ultraviolet) and IR (infrared) ranges and high light transmittance in the visible range. Such glass compositions are thus useful, for example, in windows and windshields in the automotive industry and also in architectural applications.
The automotive industry, for a number of years, has desired glass having grey color (sometimes called xe2x80x9cneutral greyxe2x80x9d) for automotive window applications. At the same time, it is also desirable for transmission in the UV and/or IR ranges of the light spectrum to be minimized. Moreover, certain Governmental regulations in the automotive industry have been known to require that visible light transmittance be at least 70% in certain vehicular windows when provided by the original equipment manufacturer of the vehicle (e.g. GM, Ford, Chrysler etc.) in the U.S.A. Accordingly, there exists a need in the automotive industry for a glass which achieves these properties (a similar need may also exist in other industries such as the architectural glass industry).
A glass window or other glass article is said to have the desirable color xe2x80x9cgreyxe2x80x9d when it has a dominant wavelength of from 435 nm to 570 nm (this dominant wavelength range defines the color xe2x80x9cgreyxe2x80x9d herein). Moreover, grey glass preferably has an excitation purity of less than about 4.5%. In certain embodiments, it may be preferable to have a dominant wavelength of from 470 nm to 570 nm, or even from 480-560 nm, with purity of from about 0.2 to 4.5%.
While glass having xe2x80x9cgreyxe2x80x9d color is often desirable, there sometimes also exists a need or desire to achieve certain levels of light transmission defined conventionally by:
Lta as visible light transmission,
UV as ultraviolet light transmission, and
IR as infrared light transmission.
Glass thickness ranges of from about 1-6 mm, more preferably from about 3-4 mm, are typically used when measuring the aforesaid characteristics. These thickness ranges are generally recognized as conventional thicknesses for glass sheets made by the float glass process, as well as recognized thickness ranges in the automotive industry.
For automotive windows (including windshields) it is often desirable for glass to have one or more of the following characteristics at any or all of the aforesaid thicknesses:
Lta: at least about 70%
UV: no greater than about 43%, more preferably no greater than 40%
IR: no greater than about 46%, more preferably no greater than about 42%
Classically formulated grey glasses often include low levels of iron (i.e., less than 0.2% total iron) along with cobalt and nickel oxides. Unfortunately, while this type of glass may achieve satisfactory coloration in certain instances, it typically suffers from undesirable solar characteristics. Certain nickel-free grey glasses combine selenium (Se) and cobalt (Co) oxide with iron oxide, but also suffer from poor solar performance characteristics.
Certain known green solar control float glasses are formulated so as to achieve desirable solar characteristics due in large part to their use of large quantities of total iron (e.g., 0.60 to 0.84% total iron). Unfortunately, the green coloration of such glasses does not always harmonize well with certain exterior automotive paints and sometimes affects vehicle interiors when viewed through the glass.
Commonly owned EP 1 041 050 (see also U.S. Ser. No. 09/277,749) discloses a grey glass composition capable of achieving the aforesaid characteristics, including the desirable color grey. In particular, EP 1 041 050 discloses a grey glass with a colorant portion including 0.5-0.8% total iron (expressed as Fe2O3), 0.5-3.0% Er2O3, and 0.0-1.0% TiO2. Moreover, the colorant portion is said to be xe2x80x9csubstantially free of seleniumxe2x80x9d (Se) and xe2x80x9csubstantially free of cobaltxe2x80x9d (Co). While the grey glass of EP 1 041 050 is an excellent glass, it is sometimes undesirable in that it requires much of the very expensive erbium oxide (Er2O3). Rather large amounts of total iron (expressed as Fe2O3) are also required in many examples.
U.S. Pat. No. 5,264,400 discloses a bronze glass including 0.2 to 3% by weight erbium (Er) in the form of Er2O3. Small amounts of Se and/or Co are also present in certain examples. Unfortunately, the glasses of the ""400 patent are bronze, not grey. This is evidenced by the dominant wavelengths in Table 2 of the ""400 patent, which are all above 570 nm. Moreover, the erbium-inclusive glasses of Examples 1-9 of the ""400 patent require large amounts of cerium (Ce), i.e., 0.40% and greater. Such high amounts of cerium are undesirable. Instead, it would be desirable if cerium could be avoided in such large doses for at least the following reason. Iron is often introduced into glass in the form of Fe2O3, part of which is reduced to FeO to achieve low IR transmittance values. Cerium, often introduced into glass in the form of CeO2, is known to oxidize divalent iron (Fe2+) to trivalent iron (Fe3+) either directly or in combination other reducing agent(s) present in the glass melt. Therefore, coexistence of iron oxide and cerium oxide will inevitably lead to a decrease in the concentration of FeO in the glass and thus will reduce the IR absorbing power of the glass.
In view of the above, it is apparent that there exists a need in the art for a new glass composition which overcomes the above problems while achieving one or more of desired grey color and desired solar management property(ies) of the particular industry in which it is to be used.
An object of this invention is to provide a grey glass (i.e., having a dominant wavelength of from 435nm to 570 nm) including a colorant portion which may include from 0.50 to 1.20%, by weight, erbium oxide (Er2O3), and from about 0.10 to 0.60%, by weight total iron (expressed as Fe2O3).
Another object of this invention is to provide a colorant portion for use in a glass composition (with a soda lime silica or other suitable base glass), the colorant portion comprising (or consisting essentially of in certain embodiments), by weight percentage:
Generally speaking, certain embodiments of this invention fulfill one or more of the above listed objects by providing a grey colored glass comprising:
a base glass portion comprising:
and a colorant portion consisting essentially of:
wherein the grey colored glass has a dominant wavelength in the range of from 435 nm to 570 nm.
In other embodiments of this invention, one or more of the above-listed objects is/are fulfilled by providing a grey colored glass comprising:
In certain exemplary embodiments, the glass composition is substantially free of cerium and/or nickel. In certain embodiments, the amount of Se may be from 0.0 to 0.0010%.
Grey glasses according to different embodiments of this invention may be used, for example, in the automotive industry (e.g., windshields, backlites, side windows, etc.), in architectural applications, and in other suitable applications.
Certain glasses according to this invention utilize soda-lime-silica flat glass as their base composition/glass, to which is added certain ingredients making up a unique colorant portion. An exemplary soda-lime-silica base glass according to certain embodiments of this invention, on a weight percentage basis, includes the following basic ingredients:
Other minor ingredients, including various conventional and refining aids, such as SO3, carbon, and the like may also be included in the base glass. In certain embodiments, for example, glass herein may be made from batch raw materials silica sand, soda ash, dolomite, limestone, with the use of salt cake (SO3) and/or Epsom salts (e.g., about a 1:1 combination of both) as refining agents. Reducing agent(s) such as Si (metallic), Si, silicon monoxide, SiO, sucrose, and/or carbon may also be used. Preferably, soda-lime-silica base glasses herein include by weight from about 10-15% Na2O and from about 6-12% CaO. While a soda-lime-silica base glass set forth above is preferred in certain embodiments of this invention, this invention is not so limited. Thus, other base glasses (e.g., borosilicate glass) may instead be employed in alternative embodiments.
To the base glass (e.g., see Table 1 above), the instant invention adds a colorant portion which causes the resulting glass to be grey in color (i.e., dominant wavelength of from 435nm to 570 nm) and achieve desirable solar management properties (e.g., low UV and IR transmission coupled with high visible transmission). In certain preferred embodiments, the resulting grey glass has a dominant wavelength of from 480 nm-560 nm (nanometers). Moreover, the resulting glass preferably has an excitation purity (Pe) no greater than about 4.5%, and most preferably from 0.2% to 4.5%.
In certain embodiments of this invention, an exemplary colorant portion that is added to the base glass is substantially free of cerium and nickel (i.e., no more than 0.0030% Ce, CeO, and/or CeO2, and no more than 0.0010% Ni and/or NiO), and is characterized as set forth in Table 2 below (in terms of weight percentage of the total glass composition):
In certain more preferred embodiments, the colorant portion may include: from about 0.20 to 0.56% total iron (more preferably from about 0.35 to 0.50% total iron); from 0.50 to 1.20% erbium oxide (including but not limited to Er2O3) (more preferably from 0.60 to 0.90% erbium oxide); from 0.0003-0.0010% Se (more preferably from about 0.0004-0.0007% Se); from 0.0007-0.0018% cobalt oxide (i.e., CoO including but not limited to Co3O4) (more preferably from about 0.0007-0.0015% cobalt oxide); from 0.0-0.70% titanium oxide (i.e., including but not limited to TiO2) (more preferably from 0.0-0.15% titanium oxide); and/or from 0.0to 1.5% boron oxide (i.e., including but not limited to B2O3) (sometimes from 0-1.0 weight % B2O3). In certain embodiments of this invention, the colorant portion is substantially free of other colorants (other than potentially trace amounts) so that the colorant portion consists essentially of the above ingredients. However, it should be appreciated that small amounts of other materials (e.g., refining aids, melting aids, and/or impurities) may be present in the glass such as chromium, manganese, molybdenum, tin, chlorine, zinc, zirconium, Si, sulfur, fluorine, lithium and strontium, without taking away from the purpose(s) and/or goal(s) of the instant invention.
The total amount of iron present in the glass and in the colorant portion thereof is expressed herein in terms of Fe2O3 in accordance with standard practice. This, however, does not imply that all iron is actually in the from of Fe2O3. Likewise, the amount of iron in the ferrous state is reported herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO. The proportion of the total iron in the ferrous state (i.e., FeO) is used to determine the redox state of the glass, and is expressed as the ratio FeO/Fe2O3, which is the weight percentage (%) of iron in the ferrous state (expressed as FeO) divided by the weight percentage (%) of total iron (expressed as Fe2O3). Thus, Fe2O3 herein means total iron and FeO means iron in the ferrous state. According to certain embodiments of this invention, the colorant portion of the glass composition herein is characterized by a redox value (i.e., FeO/Fe2O3) of from 0.10 to 0.25, more preferably from 0.13 to 0.20.
Moreover, it is noted that glass according to this invention is often made via the known float process in which a tin bath is utilized. It will thus be appreciated by those skilled in the art that as a result of forming the glass on molten tin in certain exemplary embodiments, small amounts of tin or tin oxide may migrate into surface areas of the glass on the side that was in contact with the tin bath during manufacture (i.e., typically, float glass may have a tin oxide concentration of 0.05% or more (wt.) in the first few microns below the surface that was in contact with the tin bath).
Glasses of this invention, as stated above, achieve a true grey or neutral grey color, as opposed to bronze or other coloring. Such a true xe2x80x9cgreyxe2x80x9d color is best defined, as aforesaid, by referring to: (1) xe2x80x9cdominant wavelengthxe2x80x9d, and/or (2) xe2x80x9cexcitation purity.xe2x80x9d In certain embodiments, glasses herein include one or more of the following CIE LAB color coordinates [Ill. C, 2 degree observer] when measured at a nominal thickness of from about 1 mm-6 mm (and preferably for most uses, at about 3 mm-4 mm):
When used in the automotive market for windows and/or windshields that must conform to certain minimal visible light transmission properties, glass articles of this invention (e.g., at 3 mm thicknesses for purposes of reference) preferably have an Lta of at least 70% and, in certain embodiments at least about 72%, and in still further instances at least about 73%; an IR transmission percentage (%) of no greater than 46%, more preferably no greater than 42%, and most preferably from 33-42%. Additionally, in certain exemplary embodiments, glasses herein have a UV transmission percentage (%) of no greater than about 43%, more preferably no greater than 40%.
The glasses of this invention achieve the above unique characteristics (i.e., desired grey color in combination with desired solar management properties, e.g., Lta, UV, IR) in base glasses (e.g., silicate glasses such as soda-lime-silica, or borosilicate glasses) through the use of the unique colorant portion which includes from 0.10 to 0.60% total iron (more preferably from 0.20 to 0.56%, and most preferably from 0.35 to 0.50% total iron-expressed as Fe2O3) in combination with a relatively low amount of erbium oxide (e.g., Er2O3), i.e., from 0.3 to 1.5%, more preferably from about 0.50 to 1.20%. Erbium acts as a pink colorant, while the FeO aspect of the total iron acts as a blue colorant. As discussed above, selenium and cobalt are also utilized in the colorant portion for coloration purposes to achieve the desired grey color. In particular, lower amounts of total iron are used in the colorant portion of glasses herein relative to certain examples in EP 1 041 050. In view of the amount of FeO at such a total iron level, it has been found that lower amounts of the costly Er2O3 are appropriate in order to achieve the desired grey coloration. It has also been found that the lower amounts of total iron may be compensated for by the use of the Se/Co color pair to induce additional absorption and improve grey coloration.
With regard to Se, in certain embodiments Se may be introduced into the glass batch in amounts of, for example, from 5-20 ppm, more preferably from 10-20 ppm. In order to increase retention of Se and to improve homogeneity of the glass through a more uniform Se distribution in the melt, compositions of this invention may use various sources of Se, such as sodium and/or calcium selenites, iron and/or cobalt selenides, and/or metallic Se powder. Moreover, while Se often combines with iron as iron selenide (FeSe) in glass to produce brown color, and does so in certain embodiments of this invention, selenium is referred to in the colorant portion herein as xe2x80x9cSexe2x80x9d which is meant to include, for example, its state as Se as well as its state in glass as FeSe. While the use of Se is preferred in the colorant portion as discussed above, it is noted that in some embodiments Se need not be present. Thus, in some embodiments, the colorant portion may include Se in the amount of 0.0 to 0.0010% by weight, more preferably from 0.0002 to 0.0010%.
Regarding cobalt (Co), this blue colorant may be added to the glass batch in amounts of, for example, 10-30 ppm. Moreover, it is believed that much of the cobalt in the glass is in the oxide state of Co3O4. However, other oxide states of CoO are also possible in glasses according to this invention. Thus, unless expressly stated to the contrary, the terms xe2x80x9cCoOxe2x80x9d and xe2x80x9cCo3O4xe2x80x9d as used herein include not only cobalt in this/these particular oxide state(s), but also include(s) cobalt which may be present in other oxide state(s).